1. Field of the Invention
This invention relates to the double-base propellants and rocket motors containing the same. In a particularly preferred embodiment of the invention, a small tactical rocket motor contains a double-base propellant having improved mechanical properties.
2. Description of the Related Art
Propellants in which the binder is formed from nitrocellulose plasticized with a nitrate ester, such as, for example, nitrocellulose plasticized with nitroglycerine and/or diglycol dinitratei are commonly known as double-base propellants. Due to the combination or inter-diffusion of oxidizing and reducing elements (which release energy through combustion) of the plasticizer and nitrocellulose, double-base propellants are known as homogeneous propellants. Advantageous properties associated with double-base propellants, including their excellent ambient mechanical properties, aging capabilities, and operational characteristics, make double-base propellants highly desirable for many rocket motor applications.
Double-base propellants have consistently been found to be problematic at elevated temperatures due to inferior mechanical properties. For example, double-base propellants are generally understood to exhibit poor high temperature tensile strength and large thermal coefficient of linear expansion (TCLE).
Mechanical strains resulting from dramatic temperature changes, which a propellant experiences in normal fabrication and use, are believed to promote fractures in the propellant grain. Propellants with very high TCLE values may be subject to high mechanical strain as the result of temperature cycling during storage. These fractures can be wide spread and significantly increase the exposed surface area of the propellant that is available for combustion reaction. Further, the amount of fracturing and the vicinities at which the fracturing occur can be unpredictable. As a consequence, the chamber pressure created during combustion of a double-base propellant grain can be increased to unanticipated levels.
To improve the TCLE of double-base propellants and circumvent the problems outlined above, it has been proposed to add solid additives such as aluminum, ammonium perchlorate (AP), or RDX to propellant grains. However, such solid materials may increase the detonation sensitivity of the double-base propellant.
It would therefore be a significant advancement in the art to provide a double-base propellant that is sufficiently mechanically robust, even at elevated temperatures, to avoid unacceptable amounts of propellant grain fracture during use, yet at the same time exhibits a reduced detonation sensitivity to impact, friction, and electrical discharge.
It is therefore one of the objects of this invention to provide a double-base propellant that may be formulated to address the aforementioned problems associated with the related art and realizes the advancement expressed above.
It is another object of this invention to provide a rocket motor engine or assembly containing the double-base propellant of this invention.
Additional objects and advantages of the invention will be set forth in the description that follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations pointed out in the appended claims.
In accordance one aspect of this invention, these and other objects are attained by the provision of a rocket motor propellant comprising a combustible double-base propellant and non-carbonized, non-graphitized polymeric fibers dispersed in the double-base propellant. The double-base propellant is formed from a composition comprising nitrocellulose and at least one nitrate ester.
The fibers contemplated by this invention are not subject to graphitization or carbonization, except possibly upon ignition of the propellant. When present in an effective concentration, the fibers reduce the friction and impact sensitivity of the propellant, provide mechanical reinforcement, particularly at high temperatures, and eliminate pinch points and areas of high concentration of force.
In accordance with another aspect of this invention, a rocket motor assembly comprising the double-base propellant of this invention is provided. The rocket motor assembly comprises a rocket motor case, a solid propellant grain contained in the rocket motor case, and a nozzle in operative association with the rocket motor case to receive and discharge combustion products generated upon ignition of the solid propellant grain. The solid propellant grain comprises a combustible double-base propellant formed from a composition comprising nitrocellulose and at least one nitrate ester. Polymeric fibers are dispersed in the double-base propellant.